There is a mixed reality (MR) technique for aligning and superimposing an image of a virtual object generated by computer graphics (hereinafter referred to as CG) on an actually-sensed image to make an observer feel as if the virtual object existed in real space (see, for example, Japanese Patent Laid-Open No. 11-84307).
There are various applications of the MR technique including, for example, a medical-assistance application in which CG of internal organs is aligned and superimposed on actually-sensed images of a patient's body surface, thereby making a doctor feel as if he/she were seeing through the body, an application in which CG of assembly procedures is superimposed on actually-sensed images of a product at a factory, thereby assisting assembly operations, and a guidance application in which place names and other names are superimposed on images of real scenery.
Incidentally, the background on which CG is superimposed does not need to be an actually photographed image and a similar effect can be achieved by displaying only CG on a translucent display member (such as a half mirror) placed in the line of sight of the observer. This method is referred to as an optical see-through method. On the other hand, the method which uses an actually-sensed image as the background is known as a video see-through method.
To make the observer experience a sensation of mixed reality without feeling a sense of incongruity, it is important to accurately align the real space serving as the background with the CG to be superimposed on it. Therefore, to superimpose CG with a reduced sense of incongruity, it is normal practice to measure the viewpoint position and orientation of the observer and then generate CG using the measured viewpoint position and orientation and a three-dimensional model of a virtual object.
The viewpoint position and orientation of the observer is provided as information which has six degrees of freedom, and thus sensors (position and orientation sensors) available to measure them are limited. Generally, magnetic sensors, optical sensors, or image sensors are used.
However, position and orientation measuring sensors including magnetic sensors and image sensors have a predetermined measurable range and can measure position and orientation only within this measurable range. Consequently, arrangement of sensors limits the viewer's allowed range of motion.
Thus, when installing sensors at a site, it is a big issue how to arrange the sensors. However, since information used by the sensors such as magnetism or light cannot be captured visually, the measurable ranges of the sensors cannot be seen visually and the sensors must be arranged by relying on experience and hunches after all. However, sensor arrangement based on hunches may not allow a planned measurable range to be secured. This is inefficient because of the need to install and adjust the sensors repeatedly.